Direction finding system



N 26, 1940- w. M. HAHNEMANN 2,223,066

DIRECTION F INDING SYSTEM Filed Feb. 4, 1938 -fireman F/I J AMPLIFIERS kECEII/E? C M PE "511 TOR.

r Patented Nov. 26, 1940 g UNITED STAil.1155.5

DIRECTION FINDING SYSTEM Walter Max llahnemann, Berlin, Germany, as-) I i signor to C. Lorenz Aktieng'esellschaft, Berlinr a; Tempelliof, Lorenzweg, Germanma company Application February 4, 1938, Serial No. 188,7 25

r In Germany February 5, 1937 C la ims. (01. 250-11) The present'invention relates to direction finding systems which operate with rotating frame aerials and in which the irregularly polarized'in- I terference wave set up on account of the night 5' a'nd twilight effect is' rendered ineffective by compensation. L .The invention consists in certain featuresof novelty over the known systems'of' the aforesaid type which will appear from the"following-de-- 1'0 scription and be pointed out *in" the appended claims, reference being' made to the accompanying drawing, in'which: 5

' Fig. 1 schematically illustrates a known direction finding frame'arrangemenmFig. 2 is the di- 1 51 rectional diagram obtained by the arrangement shown inFig. 1; Fig. 3 schematically illustrates one modification of a known arrangement for direction finding; 'Fig. 4 is the directional diagram of the arrangement according to Fig.3; 120 Fig. 5 schematically demonstrates one embodi ment according to the invention; Fig'.6 is a schematical representation of a. compensating ar rangement of the invention; while Fig. Tshows a"*modification of'the' design which is shown .325 in Fig. 6.

' Several attempts have been made in the past to eliminate direction-finding errors which "occuron account of the night and twilighteifect,

Fig. 1, for example, illustrates an arrangement which employs two rotating frame'aerials I and 2 interconnected in opposition'andlocated in one plane, The voltage applied to the associated direction finding receiver E is given by i the difference between the transit times which occur in reception with the frame aerials land 2.

Falsely polarized waves reach these frames in their minimum positions, that is to say, at zero difference so that the voltages produced in' these frames compensate each other and only the voltage of the'ground wave of aberration freedom remains active. However, the above described arrangement involves the disadvantage that the overall directional diagram which is the product of the two individual directional diagrams of.

,45 the frames is a cos -function as illustrated in Fig. I The "direction finding minimum is not dis- *tinctly marked so that its sharpness becomes rather poor. The use of the last mentioned arrangement introduces the further disadvantage 50 that the useful voltage which the normally powith respect to the frame aerial. ly polarized vector gives rise tovoltages in .the

dipoles and in. the direction finding frame andi level. Possibilities for j'increasing the. direction finding voltages require a largely extended base common to both frames, and-this measure in turn provides cumbersome operation.

Attempts have also been made to eliminate the 5 lack of direction 'finding sharpness under which such arrangements suffer on account ofrthe cosfunction. It has thus'been'proposed to substitute the coplanar frames above referred to by two frameaerials in parallel with one another as illustrated in "Fig. 3, in which case a directional characteristic of the'shape indicated in Fig. '4 has beenv obtained' Indeed; this diagram. possesses readily distinguished minimum points, but an ambiguity must betaken in account withrespect 1-5 to the zero points, four of which appear. Q

In addition to the direction finding'systems heretofore described, methods are known which employ one frame aerial for'the direction finding and one." or two horizontaldipoles positioned above or below said frame aerial, the dipoleor dipoles being connected in electricalopposition The abnormal- I these voltages may be mutuallybalanced by suit-. ably dimensioning the different elements confcerned. However, this type of direction finding device involves the fundamental disadvantage of being limited exclusively to the short or'ultra-ag short range of waves. An operation in the range of long waves'would require dipolellengths which wouldrma'ke .rotatability of the direction finding frame aerials impossible. Still another disadvantage prevails in connection with this method, 5

' vi'z., that the useful voltage impressed. upon the.

same properties as normal direction finding de- 4 'vices,whether space waves are incident or not,

while interferences on account of irregularly polarized waves are reliably eliminated. The inventive arrangement is characterized by the pro-,

"vision of two auxiliary frame aerials located in the same vertical plane as the main'directi'on finding frame. 'These two auxiliary frames, one of which is positioned above and the other below the main frame, are interconnected in electrical opposition and associated with the main frame in such a manner that a voltage produced in the last mentioned frame on account of an irregularly polarized wave is compensated by a second voltage of equal magnitude and opposite phase simultaneously produced in the auxiliary frames.

This arrangement is hereinafter more precisely disclosed in conjunction with the Figs. to '7. Referring to Fig. 5, the main direction finding frame aerial I and the auxiliary frame aerials 2 and 3 positioned respectively above and below the main frame aerial are mounted on a vertical rotatable shaft 4 common thereto; The two auxiliary frames 2 and 3 are interconnectedin electrical opposition so as to mutually compensate voltages set up by a normally polarized vector (ground Wave). On rotating the frame aerial assembly about the axis of the shaft 4, the two auxiliary frames 2 and 3* receive without transit time difference, in other words, the useful voltage is Zero whatever position the frames at-' tain. Consequently, only the direction'finding voltage being induced in the main frame serves for 'determining the direction of the ground Wave. An irregularly polarized wavewhich reaches the frame-assembly at an optional angle of incidence produces a voltage in the auxiliary frames which depends upon the transit time difference of reception of the frames 2 and 3 and with the same conclusiveness, a further voltage is set up also in the main frame I. These two voltages may be brought to the same magnitude and into a mutually compensating relation by suitably dimensioning the frames and the interspaces therebetween, so that merely the useful voltage set up by the normal wave component remains active at the main direction finding frame I.

Fig. 6 demonstrates one embodiment of a compensating circuit arrangement according to the invention. The auxiliary frames 2 and 3" are connected in electrical opposition one to another and-in series with the main frame L. This arrangement providesthe advantage that the entire frame assembly may be tuned conjointly, e. g.', by the agency of the condenser 4. The total frame assembly mounted on a rotatable shaft 5 common thereto is electrically associated with'the direction finding receiver E. The voltages which are adapted to compensate each other are balanced by suitably adjusting the distance d between the auxiliary frames, and the open or free area of the main frame. I. I

A further possibility for securing balance comprises the insertion of amplifiers which operate without introducing any degree of phase shift. Such an arrangement is shown in Fig. 7 by way of an example. The voltages produced in the direction finding frames are amplified independently of one another in three separate amplifiers 6, l and 8, and then applied to a compensating device 9 which effects compensation between the voltages from the main frame and from the two auxiliary frames. It is significant that no phase shift is introduced in these amplifiers. This measure permits the distance d between the two auxiliary frames to be kept rather short so that the direction finding system becomes adequate size.

The directional diagram and the useful direction finding voltage obtained according to the method above described are determined by the properties of the main frame aerial I, whether irregularly polarized waves are present or not. The double-circular diagram of the main frame I thus constitutes the directional diagram of the system, that is to say, the sharpness of direction finding is very high on account of the strongly marked minimum, and the direction finding voltage merely depends upon the open or free area of the main frame. The voltage of the auxiliary frames cannot affect the direction finding voltage in a decreasing sense since the potentials produced in the auxiliary frames by the ground wave compensate each other.

The possibility for compensating the falsely polarized wave at each and every position of the frame assembly is specifically advantageous because prew'ously known methods permit cancellation to'be effected exclusively when the frames obtain position.

What is claimed is:

l. A direction finding system comprising a vertical rotatable shaft, a main frame aerial mounted on said shaft, a first auxiliary frame aeriaLfixed on said shaft above the main frame, a second auxiliary frame aerial fixed on said shaft below the frame, circuit means connecting said first; and said second auxiliary frames in electrical opposition, and coupling means between said circuit and said main frame aerial, the aforementioned elements being so constructed and arranged that a voltage set up in said main frame in response to an incident irregularly polarized wave is compensated by a second voltage of equal magnitude and opposite phase simultaneously produced in said auxiliary frames.

2. A direction finding system according to claim 1, in whichsaid circuit includes the main frame in series with said oppositely interconnected auxiliary frames.

3. A direction finding system according to claim 1, having means for conjointly tuning said main and said auxiliary frame aerials.

4. A direction finding system comprising a vertical rotatable shaft, a main frame aerial mounted on said shaft, a first auxiliary frame aerial fixed on said shaft above the main frame, a second auxiliary frame aerial fixed on said shaft below the main frame, a circuit connecting said first and said second auxiliary frames in electrical opposition and a connection between said circuit and the main aerial so constructed and arranged that a voltage set up in said main frame in response to an incident irregularly polarized wave is compensated by a second voltage of equal magnitude and opposite phase simultaneously produced in said auxiliary frames, and amplifying means connected to separately amplify the voltages produced in said main and auxiliary frames.

5. A direction finding system according to claim 4, in which said amplifying means are constructed WALTER IMAX HAHNEMAN N 

